ORIGINAL ARTICLE Correspondence: Roland E. Akhigbe, Department of Physiology, College of Medicine, Ladoke Akintola University of Technology, Ogbomoso, Nigeria. E-mail: akhigberoland@gmail.com Keywords: ejaculation, erectile dysfunction, fertility libido, mount, sexual vigour Received: 12-Sep-2019 Revised: 6-Oct-2019 Accepted: 14-Oct-2019 doi: 10.1111/andr.12717 Assessment of sexual behaviour and fertility indices in male rabbits following chronic codeine use A. F. Ajayi and R. E. Akhigbe Department of Physiology, College of Medicine, Ladoke Akintola University of Technology, Ogbomoso, Nigeria ABSTRACT Background: Codeine is the latest trend of drug abuse, particularly in Nigeria and regarded as the gateway to the abuse of other substances. Objectives: The present study examined the effects of graded doses of codeine on sexual behaviour and fertility profile. Materials and methods: Rabbits were either administered normal saline (0.2 mL), 4mg/kg b.w of codeine (low dose), or 10mg/kg b.w of codeine (high dose) p.o for 6 weeks. Results and discussion: Findings of the study showed that codeine administration significantly increased libido as witnessed by significantly short mount latency (ML), intromission latency (IL), post-ejaculatory interval (PEI) and significantly increased mount frequency (MF), intromission frequency (IF) and ejaculation latency (EL). Furthermore, codeine caused a marked rise in penile reflexes evident by a significant increase in erections, quick flips, long flips and total penile reflexes. However, copulatory efficiency and fertility index were significantly lower in codeine-treated groups when compared with the control. Serum levels of testosterone were also significantly lower in the treated groups. Conclusions: The present study demonstrates that codeine-induced enhancement of sexual performance is via a testosterone-in- dependent mechanism. It also reveals that although codeine enhances copulatory locomotor activity, it is a potential risk factor for infertility. INTRODUCTION Sexual behaviour is a fundamental principle of reproduction. It includes mating, fertility, conception and procreation (Fouche et al., 2015; Tang et al., 2017). Several substances have been reported to influence sexual behaviour and performance. A typi- cal class of drug that has been reported to affect sexual beha- viour is the opioids. Tramadol, a common opioid, has been reported to impair sperm quality as well as induce testicular lipid peroxidation (Nna & Osim, 2017). Tramadol also caused a significant decline in Leydig cells activities (Nna et al., 2017) with a possible reduction in testosterone biosynthesis. Although tra- madol has been reported to improve premature ejaculation but adversely affect male reproduction (Hashem et al., 2014; Mar- tyn-St James et al., 2015; Nna et al., 2017), it is structurally differ- ent from other members of the opioid family (McMillan, 2018). Leon & Wexler (1973) documented the relationship between heroin addiction and sexual behaviour. They found out that her- oin addiction impaired sexual desire and orgasm. They also reported a negative association between heroin addiction and the frequency of intercourse, masturbation and ejaculation. Although, sexual dysfunctions in opioid addicts both in the drugged and abstinent state have been reported (Cushman, 1972; Martin et al., 1973), Kumar et al. (1978) observed that morphine led to increased sexual contacts but impaired ejaculation in rats. These changes were abrogated following morphine withdrawal. They observed that mounting responses and the amount of time spent in social and sexual interaction with receptive female were reduced (Mumford & Kumar, 1979). Methadone has also been reported to suppress sexual behaviour and reduce the frequency of ejaculation among males (Crowley & Simpson, 1978). There is a global opioid epidemic with a rise in the non-pre- scription use of the drug. In 2016, over 11 million people in the United States (12.5% of prescription users) were reported to be involved in non-medicinal prescription opioid use (NSDUH, 2017). Similarly, in Canada, these molecules are the second most prevalent drugs used illicitly (Fischer & Rehm, 2018). Codeine, a © 2019 American Society of Andrology and European Academy of Andrology Andrology, 2020, 8, 509–515 509 ISSN: 2047-2919 ANDROLOGY